This code is designed to read and display the ambient...

September 3, 2025 at 05:05 PM

#include <xc.h>
#include "config.h"

// ==========================
// Definitions
// ==========================
#define DIGIT1 LATCbits.LATC0   // First digit select
#define DIGIT2 LATCbits.LATC1   // Second digit select

#define STORE_BTN PORTDbits.RD0 // Store button
#define READ_BTN  PORTDbits.RD1 // Read button

// 7-seg digit patterns (common cathode)
const unsigned char SSD_digits[10] = {
    0x3F, // 0
    0x06, // 1
    0x5B, // 2
    0x4F, // 3
    0x66, // 4
    0x6D, // 5
    0x7D, // 6
    0x07, // 7
    0x7F, // 8
    0x6F  // 9
};

// ==========================
// ADC Functions
// ==========================
unsigned int readADC(void) {
    ADCON0bits.GO = 1;               // Start conversion
    while(ADCON0bits.GO);            // Wait until done
    return ((ADRESH << 8) + ADRESL); // Return 10-bit result
}

int readTemperature(void) {
    unsigned int adc_val = readADC();
    // LM35: 10mV/°C ; with Vref=5V and 10-bit ADC: 1 step ≈ 4.88mV
    return (int)(adc_val * 0.488);   // Convert to °C
}

// ==========================
// SSD Functions
// ==========================
void sendToSSD(int digit) {
    LATB = SSD_digits[digit]; // Send to segments
}

void displayNumber(int num) {
    int tens = (num / 10) % 10;
    int ones = num % 10;

    // Show tens
    DIGIT1 = 1;
    sendToSSD(tens);
    __delay_ms(5);
    DIGIT1 = 0;

    // Show ones
    DIGIT2 = 1;
    sendToSSD(ones);
    __delay_ms(5);
    DIGIT2 = 0;
}

// ==========================
// Main
// ==========================
void main(void) {
    // I/O setup
    TRISA = 0x01;    // RA0 = analog input
    TRISB = 0x00;    // PORTB = SSD segments
    TRISC = 0x00;    // RC0, RC1 = digit select
    TRISD = 0xFF;    // RD0, RD1 = buttons (inputs)

    // ADC setup
    ADCON1 = 0x0E;   // AN0 analog, others digital
    ADCON2 = 0xA9;   // Right justified, 8TAD, Fosc/8
    ADCON0 = 0x01;   // Enable ADC, channel 0

    int temp = 0;
    int last = 0;

    while(1) {
        // Read temperature and show it
        temp = readTemperature();
        displayNumber(temp);

        // Store button
        if(STORE_BTN == 0) {
            last = temp;             // Save current temperature
            __delay_ms(300);         // Debounce delay
        }

        // Read button
        if(READ_BTN == 0) {
            // Show stored value instead of live temperature
            for(int i=0; i<200; i++) {
                displayNumber(last);
            }
            __delay_ms(300);
        }
    }
}

// ==========================
// SD Card Placeholders
// ==========================
// Later we add SPI + FAT FS here
void saveToSD(int t) { /* TODO */ }
int readFromSD(void) { return 0; }

This code is designed to read and display the ambient temperature from a sensor (likely an LM35 analog sensor), show it on a 7-segment display, and support storing and recalling the last temperature reading using push buttons. Below is a breakdown of its functionality:

1. Hardware Setup

Analog Temperature Sensor Connection:
- Analog temperature data is read via RA0 (analog input, AN0 pin) using the PIC microcontroller's ADC (Analog-to-Digital Converter).
7-Segment Display (SSD):
- A 2-digit 7-segment display is connected to PORTC for digit selection (DIGIT1, DIGIT2) and PORTB to control segment LEDs through predefined digit patterns (SSD_digits).
Buttons:
- Two buttons are used:
  - STORE_BTN (connected to RD0) saves the current temperature reading.
  - READ_BTN (connected to RD1) recalls and displays the last stored value.

2. ADC (Analog-to-Digital Conversion):

The readADC function configures and starts ADC conversion to read temperature data from the sensor.
Conversion is based on the LM35 characteristics (10 mV/°C):
- LM35 output is scaled to degrees Celsius using the (adc_val * 0.488) formula to compute temperature in integer form.

3. 7-Segment Display Control:

Two digits of the display are alternately activated (using DIGIT1 and DIGIT2) to display values by multiplexing. The function:
- displayNumber(int num) splits the input into tens and ones digits and sends the corresponding segment patterns (SSD_digits) to PORTB for each digit.
- A brief delay (__delay_ms) ensures both digits are shown in sequence quickly enough to appear simultaneous to the human eye.

4. Button Handling:

Button presses are read from STORE_BTN and READ_BTN (inputs on RD0 and RD1).
- If STORE_BTN is pressed, the current temperature is saved in the last variable.
- If READ_BTN is pressed, the stored temperature (last) is displayed on the SSD for a fixed duration (via repeated calls to displayNumber()).

5. Main Loop:

Continuously:
- Reads live temperature and displays it on the 7-segment display.
- Checks for button presses to allow storing or recalling temperatures.
- Implements simple debounce logic with a short delay after each button press (__delay_ms(300)).

6. SD Card Placeholder:

The saveToSD() and readFromSD() functions represent planned functionality for storing temperature data on an SD card (e.g., via SPI). These functions are placeholders and are not yet implemented.

Summary:

The purpose of this code is to measure temperature with an LM35 sensor using the PIC microcontroller, display it dynamically on a 2-digit 7-segment display, and provide functionality to store and recall the last measured temperature value using external buttons. Additionally, it includes provisions for future extensions with SD card storage.

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